Abnormalities of arterial vasoreactivity have been linked to a multitude of cardiovascular disease risk factors, have been shown to improve with risk factor intervention, and have been associated with prevalent coronary artery disease. Many of these observations have used as the index of vasoreactivity flow-mediated arterial dilation, a non-invasively measured parameter uniquely suited for epidemiologic investigation; this index, however, has not been tested for its association with incident coronary heart disease (CHD). Previously flow-mediated brachial arterial vasoreactivity has been quantified by a single measurement of arterial dilation measured at a fixed point in time following increase of blood flow. Bowman Gray has developed a new method for quantifying brachial artery vasoreactivity that promises to markedly enhance the informativeness of the procedure by identifying not only the maximum artery responsivity but also the time to maximum response. The proposed study will augment data already being collected in the Cardiovascular Health Study (CHS), a multicenter NIH funded population based study of risk factors and their relation to prevalent and incident symptomatic CHD and other vascular disease as well as subclinical vascular disease (e.g., asymptomatic atherosclerosis). The CHS population was initially age 65 and older (1989-1990), and will undergo its 9th yearly examination from June, 1997 through June, 1998 (n=about 3000 participants). The investigators propose to add a measure of flow-mediated brachial artery vasoreactivity to this examination. Analysis will quantify associations between flow-mediated brachial artery vasoreactivity and incident CHD over 3 years. Also of interest will be associations of vasoreactivity with cardiovascular disease risk factors and with other indices of subclinical vascular disease. The investigators state that it is likely that flow-mediated brachial artery vasoreactivity, since it provides an index of a different dimension of vascular disease than those provided by B-mode ultrasound or ankle-arm index, will be independently related to incident CHD.